#include<bits/stdc++.h>
#define ONLINE_JUDGE
#define ll long long
#define ull unsigned long long
using namespace std;

const int N = 1e6 + 10, INF = 0x3f3f3f3f;

int n;
vector<int> a;

void solve()
{
    cin >> n;
    int t1, t2, t3;
    t1 = t2 = t3 = 0;
    for (int i = 0;i < n;i++) {
        int x; cin >> x;
        a.push_back(x);
        if (x == -1) t1 = 1;
        if (x == 0) t2 = 1;
        if (x == 1) t3 = 1;
    }

    if ((t1 && t3) || count(a.begin(), a.end(), 0) == n) cout << "YES";
    else cout << "NO";
}

signed main()
{
    // ios::sync_with_stdio(0);
    // cin.tie(0);cout.tie(0);
#ifndef ONLINE_JUDGE
    std::istringstream in(R"()");
    std::cin.rdbuf(in.rdbuf());
#endif
    int T = 1;
    //cin>>T;
    for (int i = 1;i <= T;i++) {
        solve();
    }
}